Expression of cell cycle proteins in frontal cortical layer V/VI in B6-R1.40 at 12 months. A–C, There was no evidence of cyclin D (A, green) observed in NeuN-positive cells (B, red) in 10-month-old B6-R1.40 animals (C, merge). At this age, neurons residing in frontal cortical layer II/III exhibit only two spots of hybridization (C, inset). D–F, Cyclin D (D, green) immunoreactivity was encountered in neurons (E, red) in R1.40 mice aged to 12 months. Overlaying the images reveals colocalization of both cyclin D and NeuN (F). FISH indicates that neuronal re-expression of cyclin D is accompanied by DNA synthesis as evidenced by four spots of hybridization (inset). G–I, No evidence of cyclin D (G, green) was observed in NeuN+ cells (H, red) in age-matched non-transgenic controls. Cell nuclei were counterstained with DAPI (blue) throughout. For each age and genotype, a total of five animals were analyzed. Scale bar, 10 μm.

Aβ oligomers induce neuronal BrdU incorporation in cortical neurons in vitro. A–I, Cultured cortical neurons were treated with Ham's F12 vehicle (Veh) (A–C), 1000 nm of Aβ1–42 monomer-rich preparations (D–F), or 1000 nm Aβ1–42 oligomer-rich preparations (G–I) in the presence of BrdU for 24 h. Cells were fixed and coimmunostained with antibodies against Map2 (A, D, G) and BrdU (B, E, H), demonstrating the induction of BrdU incorporation in Map2-positive cells in the oligomer-rich preparations but not the monomer-rich or vehicle control (C, F, I, merged images). Scale bars, 10 μm. G–I, Insets, Higher magnification of the BrdU-positive, Map2-positive cell in the oligomer-rich treatment group. J, K, Quantification of the percentage of BrdU-positive/Map2-positive cells in Aβ monomer-rich and oligomer-rich preparations. Cortical neurons were exposed to either vehicle or increasing concentrations (50–1000 nm) of either monomer-rich (J) or oligomer-rich (K) preparations for 24 h. Treatment with oligomer-rich preparations at concentrations >100 nm resulted in a statistically significant increase in the percentage of BrdU-positive cells (p = 0.0001). L, Immunoneutralization of Aβ oligomers with the addition of the Aβ oligomer-specific antibody NU2 (100 nm) resulted in a five-fold reduction in BrdU incorporation (n = 3; p = 0.0325) in the neuronal cultures exposed to 100 nm of Aβ oligomer-rich preparations, to levels similar to the vehicle control (the same 100 nm control was used for experiments in K and L). At the same concentration, addition of nonspecific mouse IgG did not have a statistically significant effect on BrdU incorporation (L).